Friend message is an addon that basically creates a way to whisper all of your friends at once. It gives functionality similar to the friend lists used on battle.net.
Friend message has a few advantages over using a chat channel to talk to your friends:
Its more configurable (messages can be displayed anywhere onscreen and with sounds!)
The message type stays each time you press enter (similar to guild/party/raid chat)
Friends can see your messages without going into a channel or having this addon
/fm to send messages to friends (works like /guild /party /raid etc)
/fmoptions to open the options menu
While this addon may not be useful to everyone, my friends and I can't seem to do without it so I figured some people out there may feel the same.